A number line is a straight line having numbers evenly placed along its length. The number line is used to see how numbers are related to each other. As you move from left to right on the number line, the numbers increase in value, and as you move from right to left, the values of the numbers decreases.
The above image is of a number line with numbers.
While subtracting on a number line, you move to the left of the number line. For example, 6 – 2 = ?
Let us use a number line to find the answer.
Here, we draw a number line and begin at number 6, which is the minuend marked on the number line. Now, when we subtract 2 from 6, we move to the left of the number line by 2 places as we count back from the subtrahend.
From the above image, you can see that by moving to the left, we land on 4 and hence, the answer is 4.
This method is also known as the “count back strategy.”
While addition is adding numbers together to create a new number, subtraction is taking a number away from another.
We can use the count on strategy on the number line to use the “addition to subtract” method. Let us look at an example of this method. If we have to solve 14 – 9, we can use the “addition to subtract” method. Imagine, what can be added to 9 to arrive at 14? The number line will be helpful here.
We start at 9 on the number line and count to 14, which gives us 5 as the answer. So, we add 5 to 9 to arrive at 14. Thus, we get the answer for 14 – 9, which is 5.
This method is useful for finding subtraction equations where we can subtract one part from the total to get the other part.
Example 1: Find 8 – 3 with the count back strategy.
Answer: Remember, when we have to subtract, we have to count back. So, we begin at the minuend 8, which is the larger number on the number line, and count back by the smaller number 3, which is the subtrahend.
Thus, 8 – 3 = 5
5 is the answer.
Example 2: 7 students are visiting a zoo. 3 of them later decided not to go. How many students are going to the zoo now?
Answer: Number of students visiting the zoo = 7
Number of students who decided not to visit = 3
We can use the number line to find the answer.
So, in the given number line, we will begin at 7 and then move 3 times to the left. This is because we are subtracting on a number line. So, that will give us 7 – 3 = 4
Thus, 4 students are visiting the zoo now.
Example 3: Find: 12 – 7 = ?
Answer: Let us use addition to subtract for this problem.
Imagine, 7 + ____ = 12
We can get the answer to that from a number line where we will mark 7 and then count till we reach 12.
The count on strategy will give us 5. So, by adding 5 to 7, we get:
7 + 5 = 12
Thus, using the addition to subtract strategy, we get 12 – 7 = 5
The answer is 5.
Example 4: A fruit seller had 12 watermelons in the morning. He sold a few watermelons, and by the afternoon, he had 5 watermelons left. How many watermelons did he sell?
Answer: Let us use the add to subtract strategy to find the difference.
According to the problem, we have to find out 12 – 5 = ?
Let us assume, 5 + ___ = 12
If we have to represent this on a number line, this is how it will look:
We begin at 5, count on till we get 12. We can see that it took 7 jumps to reach 12.
So, 5 + 7 = 12
Thus, 12 – 5 = 7
The fruit seller sold 7 watermelons.
Number lines are not only useful for kids, but teachers and parents as well. A number line provides a visual representation of numbers and, as a result, acts as a visual math aid. Number lines make it easy for children to count numbers, compare them, and engage students in addition, subtraction, and multiplication.
While using a number line for subtraction, the numbers get smaller as you move to the left.